Add translated values to DWC cores/extensions

[MattBlissett]

Via Crowdin, translations of Darwin Core are now appearing in https://github.com/tdwg/rs.tdwg.org/blob/master/terms/terms-translations.csv

#122 handles the vocabularies, which are straightforward as the schema already supports translations.

For the core/extensions, the schema does not support translation. We either need to extend the schema (ensuring old IPTs continue to work) or use a different method — for example, there's an RDF file from an old attempt to get translations here, see gbif/ipt#892.

Also see gbif/ipt#1729